Method and apparatus for driving neon tube to form luminous bubbles and controlling the movement thereof

ABSTRACT

According to the present invention, a portion of an applied commercial AC supply (60 Hz) is rectified, filtered and a controllable oscillator in a pulse width modulator chip serves as a signal generator which has both duty cycle and frequency control adjustments. An output signal is coupled via an impedance matching circuit to the input primary winding of a signal transformer having a pair of secondary windings which drive a pair of tandem connected electronic switches which, in turn, are connected across a second DC supply which has a high direct current voltage derived from the input AC line voltage (110-120 V AC 60 Hz). A pair of tandem connected capacitors is connected across the DC supply and an intermediate point between the tandem connected electronic switches is connected to one end of the primary winding of a high voltage output transformer and a second intermediate point between the two tandem connected capacitors is connected to the opposite end of the primary winding of the high voltage output transformer so that on alternate half-cycles of the input signal coupled to the signal transformer from the impedance matching transistor switches is used to alternately drive the gate electrode of the electric switches. A series of control sequences for the switches is stored in a memory, and a microprocessor is programmed to selectively retrieve one or more control sequences so as to cause one or more neon tubes to go through a predetermined program of movements. A ground-fault sensing shut-off circuit is connected to one of the output terminals of the high voltage output transformer and includes comparator circuitry which is capable of sensing when a person, for example, touches one of the output terminals of the high voltage output electrode and disable the electronic switches.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION

In Kayser U.S. Pat. No. 1,939,903 and Becquemont U.S. Pat. No.,2,091,953, neon tubes are driven in such a way that the luminousdischarge has the appearance of brilliant luminous balls or bubblesseparated by dark spaces and appearing to move in the interior of thetube from one electrode to the other. In Kayser, an oscillating currentis applied to each end of the neon tube with one of the tube ends beinggrounded and the direction of travel of the luminous span issuing fromthe non-grounded end of the tube is varied by varying thecharacteristics of the oscillating current. In the Kayser patent, a highfrequency current has the voltage level thereof varied in a slow andprogressive manner according to the apparent movement and development ofthe bubbles and then the high frequency current is shut-off and a lowfrequency industrial current is applied in a slow and progressive mannerso that the main voltage of the oscillating current is varied. InBecquemont, a high frequency alternating current is applied to theelectrodes at a sufficient frequency to produce the luminous bubblesseparated by dark regions and a portion of the alternating current isrectified and superimposed on the applied alternating current. In yetanother prior art system, a frequency of between 1500 and 4000 Hz isproduced and the symmetry of the current applied to the tube is adjustedeither by adjusting the clipping one of the peaks of a drivingsinusoidal wave or by producing a substantially square wave voltage andadjusting the duty cycle thereof. Such a system is disclosed in KennanC. Herrick PCT/U.S. Pat. No. 86/00851, International Publication No.W086/06572, incorporated herein by reference application entitled"Apparatus and Method for Forming Segmented Luminosity in Gas DischargeTubes".

The Herrick PCT application discloses regulation of the symmetry of theresultant tube current, i.e., regulation of the net current flow betweenthe electrodes. The resultant or net current flow through the tube isregulated so as to control the movement of these alternating light anddark regions lengthwise along the tube. Regulation of the net currentflow may be accomplished either by imposition of a DC current across theelectrodes in addition to the AC signal, or by use of an AC signalhaving an asymmetric wave form. Asymmetry of the wave form may bemeasured by determining the DC voltage across a capacitor connected inseries with the gas discharge tube, and this measurement may be appliedin a feedback loop to control the degree of asymmetry and hence controlthe rate of movement of the illuminated regions lengthwise along thetube. In a further variant, the tube may be provided with a midpointelectrode to provide net current flows either from the end electrodestowards the midpoint or from the midpoint towards the end, withcorresponding movement of the light and dark regions towards or awayfrom the midpoint.

THE PRESENT INVENTION

According to the present invention, a portion of an applied commercialAC supply (60 Hz) is rectified, filtered and applied to a commerciallyavailable semi-conductor chip element which has a controllableoscillator serving as a signal generator and which has both duty cycleand frequency control adjustments. The logical output signal is coupledvia an impedance matching circuit to the input primary winding of asignal transformer. The signal transformer has a pair of secondarywindings which are used to drive a pair of tandem connected FET switcheswhich, in turn, are connected across a second DC supply which has a highdirect current voltage derived from the input AC line voltage (110-120 VAC 60 Hz).

A pair of tandem connected capacitors is connected across the DC supplyand an intermediate point between the tandem connected FET switches isconnected to one end of the primary winding of a high voltage outputtransformer and a second intermediate point between the two tandemconnected capacitors is connected to the opposite end of the primarywinding of the high voltage output transformer so that on alternatehalf-cycles of the input signal coupled to the signal transformer fromthe impedance matching transistor switches is used to alternately drivethe gate electrodes of the FET switches.

A series of control sequences for the FET switches is stored in amemory, such as a ROM or PROM, magnetic disk or tape or an opticalmemory, or a combination thereof, and a microprocessor is programmed toselectively retrieve one or more control sequences so as to cause theneon tube to go through a predetermined program of movements. In thisregard, a plurality of neon tubes can be controlled in any predeterminedpattern or sequence of luminous bubble movements from the same or asimilar memory. Thus, in one neon tube the luminous bubbles can becontrolled to move first in one direction at one speed, then in anopposite direction at the same or a different speed and then bestationary (zero velocity) for a predetermined time while the luminousbubbles in one or a plurality of other tubes of widely differing shapeand curvatures are simultaneously controlled to go through theirrespective patterns of movements.

A ground-fault sensing shut-off circuit is connected to one of theoutput terminals of the high voltage output transformer and includescomparator circuitry which is capable of sensing when a person, forexample, touches one of the output terminals of the high voltage outputelectrode. This condition is sensed and used to operate a thyristorswitch which shunts or by-passes the primary winding of the signaltransformer to thereby terminate the operation of the FET switches andthereby terminate the generation of high voltages in the secondarywindings of high voltage output transformer.

As used herein, the term "neon tube" includes tubes filled with gasesother than neon.

The above and other objects, advantages and features of the inventionwill become more apparent when taken in conjunction with theaccompanying drawings wherein:

FIG. 1 is a circuit diagram incorporating the invention,

FIG. 2 is a modification of the circuit diagram shown in FIG. 1illustrating the embodiment of the invention wherein a plurality ofseparate neon tubes are separately driven and controlled via a storedmemory and a microprocessor coupled to same and to the separate drivingcircuits.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the circuit diagram shown in FIG. 1, an AC supply 5supplies alternating current through a choke filter 6 and fuse resistor7 to the primary winding 8 of transformer T3. A varister 9 stabilizesthe input voltage. Transformer T3 is a step down transformer and appliesa low AC voltage to a bridge rectifier 11 which has a pair of filtercapacitors 12-1, 12-2 on the output thereof, and a zener diode 13 forstabilizing the output voltage, preferrably at about 30 volts DC. Aswitch mode pulse width modulation control circuit 14 (a MotorolaMC34060 or MC35060) has an oscillator therein (not shown) connected toan external pulse width modulation control circuit constituted byresistors 16-1, 16-2 and potentiometer 16-3 and an external frequencycontrol circuit constituted by capacitor 15C and potentiometer resistor15R which permits the potentiometer to adjust the resistance leg andthereby adjust the frequency of the internal oscillator in chip 14. Theoutput on terminal 9 has an internal transistor supplying output to theintermediate point between bias control resistor 14-B and couplingresistor 17.

The lower end of coupling resistor 17 is connected to the base inputs ofa pair of tandem connected complementary emitter follower NPN-PNPtransistors Q1 and Q2 which provide a low impedance drive circuit to theinput of winding 20 of signal transformer T1 via a coupling capacitor19C and resistor 19-R. Transformer T1 has a pair of secondary windings21 and 22 which have a back-to-back zener diodes 23 connectedthereacross and with the signals therefrom being used to drive the gateelectrodes of FET transistors 25 and 26 respectively. A further bridgerectifier 24 rectifies the AC line voltage from source 5 and has afilter capacitor 24-C conected thereacross for filtering purposes. (Inthis regard, the separate supply constituted by transformer T3 andbridge rectifier 11 can, if desired, be eliminated and a voltage dividerused to supply the lower DC voltage to supply the pulse width modulatorchip 14 with 30 volts).

The FET transistors 25 and 26 have their drain-source electrodesconnected in series or tandem relation across the high voltage supply(about 170 volts) and, a pair of capacitors 27, 28 are likewiseconnected in tandem across the high voltage supply. The intermediatepoint IP1 between the tandem connected FET transistors 26 and 27 isconnected to one end of the primary winding 29 of high voltage outputtransformer T4 and the intermediate point IP2 between capacitors 27 and28 is connected to the opposite end of primary winding 29 of transformerT2. Thus, when the input signal current flowing through transformerwinding 20 is in one direction, one of transistors 25 will be gated onto cause a current to flow through winding 29 in one direction and whenthe direction of current flow through transformer winding 20 is in theopposite direction, a further signal is generated in the secondarywinding of one of transformer windings 21 and 22 to trigger the otherFET transistor (and the opposite FET transistor is biased off byopposite polarity signals in the other secondary winding of transformerT1) on and thereby cause an opposite direction of current flow throughtransformer winding 29. Thus, by modulating the width of the pulsesand/or the frequency of the pulses from pulse width modulation controlcircuit 14, one is able to control both the direction and speed of theluminous bubbles flowing in the neon tube NET.

A coupling capacitor 31 in the lower lead from secondary winding 30 hasa pair of back-to-back diodes connected thereacross and adjacent theneon tube NET is coupled through a zener diode capacitor circuit 32 tothe input of a ground-fault sensing circuit which includes a pair ofcomparison resistors 36-1, 36-2 which receive, via a further fixedresistor, a selected reference voltage. The voltage on the output ofwinding 30 is sensed across resistor 37 and comparator 33 compares thisagainst the reference voltage to detect a change in that voltage. Upondetecting a change in that voltage, a signal is applied through theresistor capacitor output thereof to a further comparator circuit 34which likewise receives via resistor 37 at the intermediate pointbetween resistors 30 and 39 the signal voltage which forms a secondcomparison. Thus, a person touching one of the electrodes on the tubeNET causes a change in the voltage such that the change is detected inthe ground-fault detection circuitry to produce an output signal viaresistor 40 and onto the gate electrode of switching thyristor pair 41.This provides a shunt bypass to signal input on the primary winding 20of transformer T1 thereby avoiding or preventing the application ofcontrol signals to the gate electrodes of the FET's 25 and 26 andthereby preventing the further generation of a high voltage until theground-fault is removed.

Referring now to FIG. 2, a plurality of neon tubes NET-1, NET-2 . . .NET-N, supplied by a high voltage transformers T3-1, T3-2 . . . T3-N,each of which are separately driven from a pair of tandem connectedswitches 25-1, 25-2 . . . 25-N, 26-1, 26-2 . . . 26-N and paralleled bya pair of tandem connected capacitors 27-1, 27-2 . . . 27-N, 28-1, 28-2. . . 28-N with the intermediate points IP1-1, IP1-2, IP2-1, IP2-2 . . .IPN-1, IPN-2 between the tandem connected switches and the tandemconnected capacitors being connected to the ends of the primary windingsP-1, P-2 . . . P-N of the high voltage output transformers T3-1, T3-2 .. . T3-N. Each of the switches is an electronic switch corresponding tothe FET switches 25 and 26 shown in FIG. 1. The drive circuitry 18-20-1,18-20-2 . . . 18-20-N for the switches is shematically shown asoperating and opening and closing of the switches 25, 26, it beingunderstood that these are representations of the electronic FET switches25 and 26 shown in FIG. 1 and the transformer circuitry related thereto.Each of the switches is driven from a pulse width modulator circuit14-1, 14-2, 14-N each of which in turn receives duty cycles (pulsewidth) and frequency adjust input signals DS and E from a microprocessor50 which, in turn, receives a sequence of control signals representing apattern corresponding to a predetermined direction, speed (includingstationary) of movement of the different luminous bubbles in each of thetubes NET-1, NET-2, NET-N, respectively. The speed can, of course, be sofast that the luminous bubbles are no longer discernable and aconventional neon light display results. Thus, the programmableread-only memory 51 is accessed by the microprocessor 50 which, in turn,supplies the different patterns (luminous bubble flow direction, speed,etc.) to the pulse width modulator circuits 14-1, 14-2 . . . 14-N tothereby simultaneously control the direction of movement rate ofmovement and/or stationary positions of the luminous bubbles in each ofthe individual tubes.

The individual tubes NET-1, NET-2, NET-N can be either stacked-up invertical order for viewing simultaneously, or serially in any sequencedesired so that many combined luminous effect can be achieved throughthe combination of the tube either in serial, parallel or stackedvertical order for viewing purposes.

While there has ben shown and described a preferred embodiment of theinvention, it will be appreciated that numerous other embodiments willbe readily apparent to those skilled in the art and it is intended thatthe accompanying claims embody within their scope those obviousmodifications that would be readily apparent to one skilled in the art.

What is claimed is:
 1. A system for driving a neon tube to form luminousbubbles or beads and controlling the motion thereof in said neon tubecomprising:a high voltage transformer having primary and secondarywindings, said secondary winding being electrically connected to saidneon tube, a high voltage DC supply having a pair of terminals, a pairof electronic switches connected in tandem across said pair ofterminals, there being a first common point between said tandemconnected electronic switches, a pair of capacitors connected in tandemacross said pair of terminals, there being a second common point betweensaid tandem capacitors, means connecting one end of said primarywindings to said first common point and the other end of said primarywinding to said second common point, means connecting the ends of saidsecondary winding to said neon tube, a control signal generator havingmeans for adjusting at least one of the duty cycle and frequencythereof, a signal transformer having primary and secondary windings, animpedance matching circuit coupling said control signal generator tosaid primary winding, and conductor means connecting said secondarywindings to said electronic switches to alternately control the on/offconditions of said electronic switches and thereby the formation andmovement of said luminous bubbles or beads.
 2. The system for driving aneon tube to form luminous bubbles or beads and controlling the motionthereof in said neon tube as defined in claim 1, wherein said controlsignal generator includes a fixed frequency pulse width modulationcontrol circuit for producing said control signal and means formodifying the pulse width of said control signal.
 3. A system fordriving a neon tube to form luminous bubbles or beads and controllingthe motion thereof in said neon tube,a high voltage transformer havingprimary and secondary windings, said secondary windings beingelectrically connected to said neon tube, a DC voltage supply having apair of terminals, a pair of electronic switches connected in tandemacross said pair of terminals, there being a first common point betweensaid tandem connected electronic switches, a pair of capacitorsconnected in tandem across said pair of terminals, there being a secondcommon point between said tandem capacitors, means connecting one end ofsaid primary windings to said first common point and the other end ofsaid primary winding to said second common point, means connecting theends of said secondary winding to said neon tube, a source of controlsignals connected to control the operation of said electronic switchesand thereby the formation and movement of said luminous bubbles orbeads, and a ground fault sensor and shut-off circuit connected to saidsecondary winding to sense a touch thereof, and switch means controlledthereby for preventing operation of said electronic switches.
 4. Thesystem defined in claim 3 wherein source of control signals includes asignal transformer having a primary winding and a pair of secondarywindings, a signal generator connected to the primary winding of saidsignal transformer, means connecting one of said secondary windings toone of said pair of electronic switches and the other of said secondarywindings to the other of said pair of electronic switches to alternatelycontrol the operation thereof.
 5. The system defined in claim 3 whereinsaid switch means is connected in shunt with the primary winding of saidsignal transformer to prevent signals from said signal generator fromoperating said pair of electronic switches.